Storage area networks, also known as SANs, facilitate sharing of storage devices with one or more different host server computer systems and applications. Fibre channel switches (FCSs) can connect host servers with storage devices creating a high speed switching fabric. Requests to access data pass over this switching fabric and onto the correct storage devices through logic built into the FCS devices. Host servers connected to the switching fabric can quickly and efficiently share blocks of data stored on the various storage devices connected to the switching fabric.
Storage devices can share their storage resources over the switching fabric using several different techniques. For example, storage resources can be shared using storage controllers that perform storage virtualization. This technique can make one or more physical storage devices, such as disks, which comprise a number of logical units (sometimes referred to as “physical LUNs”) appear as a single virtual logical unit or multiple virtual logical units, also known as VLUNs. By hiding the details of the numerous physical storage devices, a storage virtualization controller advantageously simplifies storage management between a host and the storage devices. In particular, the technique enables centralized management and maintenance of the storage devices without involvement from the host server.
Performing storage virtualization is a sophisticated process. By way of comparison, a fibre channel switch does relatively little processing on the various command and data frames which pass through it on the network. But a storage virtualization controller must perform a much greater amount of processing than a fabric channel switch in order to convert the requested virtual storage operation to a physical storage operation on the proper storage device or devices.
In many instances it is advantageous to place the storage virtualization controller in the middle of the fabric, with the host servers and controllers arranged at the outer edges of the fabric. Such an arrangement is generally referred to as a symmetric, in-band, or in-the-data-path configuration. However, this configuration is generally problematic if the controller cannot operate at the specified data rate of the fabric. In the case of fibre channel, for example, this data rate is at least 1 gigabit per second. If the controller is not capable of operating at the specified data rate, traffic on the network will be slowed down and the overall throughput and latency deleteriously reduced.
For these and other reasons, there is a need for the present invention.